Test Oracle 11gR2 Express Edition as part of a CI-pass

[PhilipTrauner]

Depends on #14.

GitHub Actions are free for public repositories, and do not count against the organizations allotted minute quota.

If compute turns out to be too slow on the official runners, it will be necessary to set up a local GitHub Actions Runner. GitHub advises against using hosted runners in public repositories, as forks could potentially run arbitrary code. Because there's value to be had in having this project be open-source, creating a secondary private repo is probably the best course of action.